Organic composite coated steel sheet and a process for manufacturing the same

ABSTRACT

An organic composite coated steel sheet having a high cosmetic corrosion resistance and excellent image clarity which is desired on, for example, the outside of an outer plate forming an automobile body. The steel sheet has a chromate layer formed on the surface of a zinc or a zinc alloy plate steel sheet, and containing a specific weight of chromium, and an organic resin film formed on the chromate layer from a mixture in specific proportions of a blocked urethane-modified epoxy resin and a rust-preventing additive, and having a thickness of 0.2 to 2 microns. The resin is a mixture in specific proportions of a modified epoxy resin (A) which consists of an epoxy resin and a polyfunctional amine, and may further contain a monoisocyanate, or phosphoric acid, and a blocked urethane (B) which consists of a high molecular weight polyol having a molecular weight of 400 or more, a polyisocyanate and a blocking agent. A process for manufacturing the strip is also disclosed.

TECHNICAL FIELD

This invention relates to a coated steel sheet with a composite layercontaining an organic substance, and having an excellent cosmeticcorrosion resistance and excellent image clarity which is also excellentin anti-powdering property, weldability and paint adhesion, and which isbeneficial for use in making automobile bodies, electric appliances,etc., and also to a process for manufacturing the same.

BACKGROUND ART

The corrosion of automobile bodies by the salts which are sprinkled onroad surfaces to prevent their freezing during the wintertime has becomea big social problem recently in North America, northern Europe, andother countries or regions having a cold winter. The use of a coatedsteel sheet having an improved corrosion resistance instead of aconventional cold rolled steel strip has, therefore, been increasing asone of the measures for improving the corrosion resistance of automobilebodies.

Examples of the coated steel sheets are organic composite coated steelsheet, as disclosed in Japanese Patent Applications laid open under Nos.Sho 64-8033 and Hei 2-15177. These steel sheets comprise a steel sheetplated with zinc or a zinc alloy, and coated with a first layer formedby a chromate coating, and a second layer formed thereon by an organiccoating composed of an organic resin which comprises a base resinobtained by adding one or more basic nitrogen atoms and two or moreprimary hydroxyl groups to the ends of molecules or an epoxy resin, apolyisocyanate compound and a blocked isocyanate compound, the organicresin film further containing specific proportions of silica and asparingly soluble chromate. These strips are excellent in corrosionresistance, weldability, anti-powdering property and paint adhesion.

The recent inclination toward high-class and original automobiles hascome to require a greater importance to be placed on the quality of apaint-finished body surface, particularly its image clarity. The organiccomposite coated steel sheet as hereinabove described has, however, thedrawback of being somewhat inferior to the conventional zinc or a zincalloy plated steel sheet in image clarity as desired of the outersurface of the outer panel of the automobile body, though it may have agood perforation corrosion resistance as required of the inner surfacesof the outer and inner panels of the automobile body. Moreover, theknown organic composite coated steel sheet cannot necessarily be said tobe capable of forming a satisfactorily cosmetic corrosion resistanceouter surface on the outer panel of the automobile body.

Under these circumstances, it is an object of this invention to providean organic composite coated steel sheet which can form an excellentcosmetic corrosion resistance and image clarity on, for example, theouter surface of the outer panel of an automobile body, and a processfor manufacturing the same.

DISCLOSURE OF THE INVENTION

The steel sheet of this invention having a composite coating containingan organic resin has a first layer a chromate layer formed on thesurface of a zinc or a zinc alloy plate steel sheet, and having acoating weight of 10 to 200 mg/m² in terms of metallic chromium, and asa second layer formed on the first layer an organic resin filmcontaining a blocked urethane-modified epoxy resin and a rust-preventingadditive in a ratio of 90/10 to 40/60 (by weight), and having athickness of 0.2 to 2 microns. The basic composition of the blockedurethane-modified epoxy resin is as shown at i) below:

i) A blocked urethane-modified epoxy resin obtained by mixing a modifiedepoxy resin (A) which comprises an epoxy resin and a polyfunctionalamine, and a blocked urethane (B) which comprises a polyol, apolyisocyanate and a blocked agent, in an A/B ratio of 95/5 to 50/50 (byweight).

The use of a modified epoxy resin obtained by adding a monoisocyanate,as well as a polyfunctional amine, to an epoxy resin enables theformation of a film having a still higher level of corrosion resistance.In this case, the composition of the blocked urethane-modified epoxyresin is as shown at ii) below:

(ii) A blocked urethane-modified epoxy resin obtained by mixing amodified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and a monoisocyanate, and a blocked urethane (B)which comprises a polyol, a polyisocyanate and a blocking agent, in anA/B ratio of 95/5 to 50/50 (by weight).

The use of a modified epoxy resin obtained by adding phosphoric acid, aswell as a polyfunctional amine, to an epoxy resin enables the formationof a film having a higher degree of adhesion to a steel strip, and animproved corrosion resistance. In this case, the composition of theblocked urethane-modified epoxy resin is as shown at iii) below:

iii) A blocked urethane-modified epoxy resin obtained by mixing amodified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and phosphoric acid, and a blocked urethane (B)which comprises a polyol, a polyisocyanate and a blocking agent, in anA/B ratio of 95/5 to 50/50 (by weight).

Silica or a sparingly soluble chromate is preferred as therust-preventing additive in the film forming the second layer. Aparticularly high level of corrosion resistance can be obtained byadding both of silica and a sparingly soluble chromate in ratios (byweight) as shown below:

    Blocked urethane-modified epoxy resin/(silica+a sparingly soluble chromate)=90/10 to 40/60, and silica/a sparingly soluble chromate)=90/10 to 10/90.

The process of this invention for manufacturing a steel sheet having acomposite coating as hereinabove described comprises chromating thesurface of a zinc or a zinc alloy plated steel sheet by coating it witha chromate solution and drying it without rinsing it with water to forma chromate layer having a coating weight of 10 to 200 mg/m² in terms ofmetallic chromium on the strip surface, coating the chromate layer witha paint composition containing a blocked urethane-modified epoxy resinselected from among i) to iii) above and a rust-preventing additive in aratio of 90/10 to 40/60 (by weight of non-volatile matter), and bakingit to form an organic resin film having a thickness of 0.2 to 2 micronson the chromate layer.

Silica or a sparingly soluble chromate is preferably used as therust-preventing additive to the paint composition. A particularly highlevel of corrosion resistance can be obtained by adding both of silicaand a sparingly soluble chromate in ratios (by weight) as shown below:

    Blocked urethane-modified epoxy resin/(silica+a sparingly soluble chromate)=90/10 to 40/60, and silica/a sparingly soluble chromate)=90/10 to 10/90.

DETAILED DESCRIPTION OF THE INVENTION

Description will now be made of the details of this invention and thereasons for the limitations made for defining it.

A zinc or a zinc alloy plated steel sheet is used as a base material. Itmay, for example, be a steel sheet plated with zinc, a Zn-Ni alloy, aZn-Fe alloy, a Zn-Mn alloy, a Zn-Al alloy, a Zn-Cr alloy or a Zn-Co-Cralloy, or a steel sheet plated with a composite layer which contains oneor more additives selected from among metal oxides, sparingly solublechromate, polymers, etc. in a layer of zinc or a zinc alloy. It may alsobe a steel sheet coated with two or more plating layers of the same ordifferent materials. The plating of the strip can be effected by anymethod selected from among electrodeposition, hot dipping andvapor-phase deposition on a case to case basis, though electrodepositionhas an advantage over the other methods for plating a cold rolled steelstrip.

The chromate layer formed on the surface of the steel sheet plated withzinc or a zinc alloy inhibits the corrosion of the steel sheet by itsself-heating effect owing to hexavalent chromic acid ions. If thechromate layer has a coating weight of less than 10 mg/m² in terms ofmetallic chromium, it cannot be expected to impart any satisfactorycorrosion resistance to the steel sheet, and if its coating weightexceeds 200 mg/m², it lowers the weldability of the steel sheet.Therefore, the chromate layer is so formed as to have a coating weightof 10 to 200 mg/m² in terms of metallic chromium. Its coating weight ispreferably from 20 to 100 mg/m² in terms of metallic chromium torealized still higher levels of corrosion resistance and weldability.

Any of the reacted-in-place, electrolytic and dried-in-place type ofchromate coating can be employed for forming the chromate layer. Thedried-in-place type chromate is, however, preferred from the standpointof corrosion resistance, since it can form a chromate layer containing alarge amount of hexavalent chromic acid ions.

The dried-in-place type chromate is carried out by coating the steelsheet plated with zinc or a zinc alloy with a solution consisting mainlyof a partially reduced aqueous solution of chromic acid, and furthercontaining one or more additives selected from among (1) to (7) below,if required, and drying it without rinsing it with water:

(1) An organic resin such as a water-soluble or -dispersible acrylic orpolyester resin:

(2) a colloid and/or powder of oxide such as silica, alumina, titania orzirconia;

(3) an acid and/or a salt thereof, such as molybdic, tungstic or vanadicacid, or a salt thereof;

(4) a phosphoric acid such as phosphoric or polyphosphoric acid;

(5) a fluoride such as zirconium fluoride, silico-fluoride or titaniumfluoride;

(6) a metal ion such as zinc ion; and

(7) an electrically conductive fine powder such as iron phosphide orantimony-doped tin oxide.

A roll coater is usually employed for coating the strip with thesolution for its chromate coating, though it is also possible to applythe solution to the strip by dipping or spraying and regulate itscoating weight with an air knife, or by roll squeezing.

The organic resin film formed as the second layer on the chromate layerinhibits the excessive dissolution of hexavalent chromic acid ions fromthe chromate layer into a corrosive environment and thereby allows thechromate layer to produce a sustained effect of preventing corrosion,and the silica or chromate added to the organic resin film furtherimproves the corrosion resistance of the steel sheet. If the organicresin film has a thickness which is smaller than 0.2 micron, sosatisfactory corrosion resistance can be expected from the steel sheet,but if its thickness exceeds two microns, it lowers the weldability andimage clarity of the steel sheet. Therefore, the organic resin film isformed with a thickness of 0.2 to 2 microns. Its thickness is preferablyin the range of 0.3 to 1.5 microns to ensure that the strip have stillhigher levels of corrosion resistance, weldability and image clarity.

The organic resin film comprises a blocked urethane-modified epoxy resinand a rust-preventing additive.

The basic composition of the blocked urethane-modified epoxy resin is asshown at i) below:

i) A blocked urethane-modified epoxy resin obtained by mixing a modifiedepoxy resin (A) which comprises an epoxy resin and a polyfunction amine,and a blocked urethane (B) which comprises a polyol, a polyisocyanateand a blocking agent, in an A/B ratio of 95/5 to 50/50 (by weight).

The use of a modified epoxy resin obtained by adding a monoisocyanate,as well as a polyfunctional amine, to an epoxy resin enables theformation of a film having a still higher level of corrosion resistance.In this case, the composition of the blocked urethane-modified epoxyresin is as shown at ii) below:

ii) A blocked urethane-modified epoxy resin obtained by mixing amodified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and a monoisocyanate, and a blocked urethane (B)which comprises a polyol, a polyisocyanate and a blocking agent, in anA/B ratio of 95/5 to 50/50 (by weight).

The use of a modified epoxy resin obtained by adding phosphoric acid, aswell as a polyfunctional amine, to an epoxy resin enables the formationof a film having a higher level of adhesion to a steel sheet, and animproved corrosion resistance. In this case, the composition of theblocked urethane-modified epoxy resin is as shown at iii) below:

iii) A blocked urethane-modified epoxy resin obtained by mixing amodified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and phosphoric acid, and a blocked urethane (B)which comprises a polyol, a polyisocyanate and a blocking agent, in anA/B ratio of 95/5 to 50/50 (by weight).

The epoxy resin which can be employed for the purpose of this inventionis, for example,

an epoxy resin obtained as a glycidyl ether of bisphenol A or F, or anovolak; or

an epoxy resin obtained as a glycidyl ether by adding propylene orethylene oxide to bisphenol A.

It is also possible to use an aliphatic, alicyclic, or polyether-basedepoxy resin. It is possible to use two or more epoxy resin together. Itis preferable from the standpoint of corrosion resistance to use anepoxy resin having an epoxy equivalent of 400 or above.

The modified epoxy resin (A) can be obtained if the glycidyl group inthe epoxy resin is reacted with a polyfunctional amine. Examples of thepolyfunctional amine include:

a primary alkanolamine such as ethanolamine, propanolamine,isopropanolamine or butanolamine;

a primary alkylamine such as propylamine, butylamine, octylamine ordecylamine; and

a polyfunctional amine having two or more active hydrogen atoms in onemolecule, such as ethylenediamine,

diethylenetriamine, tetraethylenepentamine, xylenediamine,aminoethylpiperazine or norbornanediaminomethyl,

It is possible to use two or more amines together. The use of analkanolamine is preferred from the standpoints of corrosion resistanceand paint adhesion.

The modified epoxy resin (A) can, for example, be produced by reactingat a temperature of 70° C. to 150° C. for 4 to 10 hours the epoxy resinand the polyfunctional amine which have been so mixed that the activehydrogen in the polyfunctional amine may have an equivalent which isfrom 1.1 to 1.8 times greater than that of the glycidyl group in theepoxy resin.

The modified epoxy resin (A) can also be prepared by reacting theglycidyl group in the epoxy resin with the polyfunctional amine, andreacting the reaction product thereof with a monoisocyanate compound.

The monoisocyanate compound can be obtained by reacting an aliphatic oraromatic monoamine with phosgene. It is also possible to use a productobtained by reacting one of the isocyanate groups in a diisocyanatecompound with an aliphatic, aromatic or alicyclic alcohol. In this case,the use of an alcohol having four or more carbon atoms is preferred fromthe standpoint of its compatibility with the epoxy resin. Examples ofthe diisocyanate compound include:

an aliphatic isocyanate compound such as hexamethylene diisocyanate ortrimethylhexamethylene diisocyanate;

an aromatic isocyanate compound such as xylylene diisocyanate,2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate; and

an alicyclic isocyanate compound such as isophorone diisocyanate ornorbornane diisocyanate methyl.

It is possible to use two or more diisocyanates compound together. Themodification of the epoxy resin with the monoisocyanate compound givesan improved corrosion resistance.

The modified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and a monoisocyanate compound can, for example, bysynthesized by reacting at a temperature of 70° C. to 150° C. for 4 to10 hours the epoxy resin and polyfunctional amine which have been somixed that the active hydrogen in the polyfunctional amine may have anequivalent which is from 1.1 to 1.8 times greater than that of theglycidyl group in the epoxy resin, adding the monoisocyanate so that itmay have an equivalent which is from 0.7 to 2.0 times greater than thatof the active hydrogen in the remaining amine, and continuing thereaction at a temperature of 30° C. to 100° C.

The modified epoxy resin (A) can also be prepared by reacting theglycidyl group in an epoxy resin with a polyfunctional amine and aphosphoric acid.

The phosphoric acid which can be employed contains at least one P-OHgroup in a molecule, and may, for example, be orthophosphoric orpyrophorphoric acid, phosphorous acid, or polyphosphoric acid. It isalso possible to use an ester of any such phosphoric acid, such as analkyl or hydroxyalkyl ester thereof. The modification of the epoxy resinwith phosphoric acid enables an improved adhesion to a steel strip.

The modified epoxy resin (A) which comprises an epoxy resin, apolyfunctional amine and a phosphoric acid can, for example, bysynthesized by reacting at a temperature of 70° C. to 150° C. for 4 to10 hours the epoxy resin, polyfunctional amine and phosphoric acid whichhave been so mixed that the active hydrogen in the polyfunctional aminemay have an equivalent which is 0.5 to 0.9 time greater than that of theglycidyl group in the epoxy resin, while the P-OH group in thephosphoric acid has an equivalent which is 0.1 to 0.5 time greater thanthat of the glycidyl group, or by reacting them stepwise.

The blocked urethane which is used for the purpose of this inventioncontains an appropriate compound which protects and renders inactive thehighly active isocyanate group in an isocyanate compound, and theisocyanate group readily recovers its activity upon heating as a resultof the dissociation of the blocking agent. It, therefore, serves as acuring agent for the modified epoxy resin.

The polyol which can be employed may, for example, be:

a divalent alcohol such as ethylene glycol, propylene glycol,1,6-hexanediol, diethylene glycol or triethylene glycol;

a trivalent alcohol such as glycerol or trimethylolpropane;

a low-molecular weight polyol such as pentaerythritol;

a polyester polyol which is polymerized form caprolactone or alow-molecular weight polyol, and dicarboxylic acid; or

a high-molecular weight polyol having a molecular weight of 400 orabove, such as polyethylene glycol, polypropylene glycol orpolytetramethylene glycol.

It is also possible to use two or more polyols together. The use of ahigh-molecular polyol is preferred, since it enables the formation of anorganic resin film having an appropriately hydrophilic property andthereby an improved affinity for a cationic electrodeposition paintwhich enables the formation of a smooth surface of electrodepositedcoatings intermediate- or top-coat surface having an excellent level ofclarity.

The polyisocyanate which can be employed may, for example, be:

an aliphatic isocyanate compound such as hexamethylene diisocyanate ortrimethylhexamethylene diisocyanate;

an aromatic isocyanate compound such as xylylene diisocyanate,2,4-tolylene diisocyanate or 2,6-tolylene diisocyanate; or

an alicyclic isocyanate compound such as isophorone diisocyanate ornorbornane diisocyanate methyl.

It is also possible to use a mixture, or adduct thereof.

The blocking agent which can be employed may, for example, be:

a compound of the phenol series, such as phenol;

a compound of the lactam series, such as ε-caprolactam;

a compound of the oxime series, such as methyl ethyl ketooxime; or

a compound of the imine series, such as ethyleneimine.

It is also possible to use a mixture of two or more such compounds.

The blocked isocyanate (B) can be obtained by reacting a mixture ofpolyisocyanate and polyol in which the polyisocyanate contains an excessof isocyanate group over the hydroxyl group in the polyol, whereby aprepolymer is produced, and protecting the isocyanate group remaining inthe prepolymer with the blocking agent. A reaction temperature of 30° C.to 100° C. is employed.

The blocked urethane-modified epoxy resin according to this inventioncan be obtained by mixing the modified epoxy resin (A) and the blockedurethane (B). They are mixed in an A/B ratio of 95/5 to 50/50 (by weightof nonvolatile matter). No A/B ratio exceeding 95/5 is desirable, as itresults in an intermediate- or top-coat surface of lower clarity. Noratio that is smaller than 50/50 is desirable, either, as it results ina lower level of corrosion resistance. The A/B ratio is preferably from90/10 to 60/40 to achieve still higher levels of surface clarity andcorrosion resistance.

An improved corrosion resistance can be achieved by adding silica and/ora sparingly soluble chromate to the blocked urethane-modified epoxyresin.

Silica promotes the formation, among other corrosion products of a zincor a zinc alloy plated steel sheet, of basic zinc chloride which is aneffective corrosion inhibitor. Moreover, silica apparently owes itscorrosion-preventing effect to the fact that it is slightly soluble in acorrosive environment and forms a silicic acid ion which serves as afilm-forming corrosion inhibitor. If the blocked urethane-modified epoxyresin and silica are employed in a ratio exceeding 90/10 by weight ofnonvolatile matter, silica does not exhibit any satisfactorycorrosion-preventing effect, but the film has a lower level of corrosionresistance. If their ratio is smaller than 40/60 by weight ofnonvolatile matter, the blocked urethane-modified epoxy resin fails tobe an effective binder, and the film has a lower level of paintadhesion. Therefore, the blocked urethane-modified epoxy resin andsilica are preferably employed in a ratio of 90/10 to 40/60 by weight ofnonvolatile matter.

The silica which can be employed for the purpose of this invention may,for example, be:

silica produced by a dry process (e.g. products of Nippon Aerosil Co.,Ltd. known as AEROSIL 130, AEROSIL 200, AEROSIL 300, AEROSIL 380,AEROSIL R972, AEROSIL R811 and AEROSIL R805);

organosilica sol (e.g. products of Nissan Chemical Industries, Ltd.known as MA-ST, IPA-ST, NBA-ST, IBA-ST, EG-ST, XBA-ST, ETC-ST andDMAC-ST);

silica produced by a wet process of sedimentation (e.g. products ofTokuyama Soda Co., Ltd. known as T-32(S), K-41 and F-80); or

silica produced by a wet process of gelling (e.g. products ofFuji-Davison Chemical Ltd. know as SYLOID 244, SYLOID 150, SYLOID 72,SYLOID 65 and SHIELDEX).

It is also possible to use a mixture of two or more types of silica.

The addition to the blocked urethane-modified epoxy resin of hydrophobicsilica having a surface rendered hydrophobic by the replacement of itssilanol group with a methyl group, etc. results in an organic film whichhas a poor affinity for a cationic electrodeposition paint. The filmdisables the formation of a smooth electrodeposited paint, and top-coatsurface from having a high level of image clarity. Therefore, the use ofsilica not having a hydrophobic surface is preferred to achieve a highlevel of image clarity.

The sparingly soluble chromate which is added to the organic film isconsidered to inhibit the corrosion of the steel sheet by discharginghexavalent chromic acid ions as a result of its slight dissolution in acorrosive environment, as is the case with the chromate layer. If theblocked urethane-modified epoxy resin and the sparingly soluble chromateare employed in a ratio exceeding 90/10 by weight of nonvolatile matter,however, the sparingly soluble chromate does not exhibit anysatisfactory corrosion-preventing effect, but the film has a lower levelof corrosion resistance. If their ratio is smaller than 40/60 by weightof nonvolatile matter, the blocked urethane-modified epoxy resin failsto be an effective binder, and the film has a lower level of paintadhesion. Therefore, the blocked urethane-modified epoxy resin and thesparingly soluble chromate are preferably employed in a ratio of 90/10to 40/60 by weight of nonvolatile matter.

The sparingly soluble chromate which can be employed for the purpose ofthis invention is, for example, a fine powder of barium chromate(BaCrO₄), strontium chromate (SrCrO₄), calcium chromate (CaCrO₄), zincchromate (ZnCrO₄.4Zn(OH)₂), potassium zinc chromate (K₂ O.4ZnO.4CrO₃.3H₂O), or lead chromate (PbCrO₄). It is also possible to use a mixture oftwo or more such salts. It is, however, preferable from the standpointof corrosion resistance to use barium or strontium chromate, or both,since they can be expected to exhibit a self-healing effect by chromicacid ions over a long period of time. The use of barium chromate whichis poorly soluble in water is preferred to minimize the dissociation ofwater-soluble chromium from the organic film during the treatment ofautomobiles prior to paint application.

The addition of both silica and a sparingly soluble chromate in specificproportions to the blocked urethane-modified epoxy resin enables thebest corrosion resistance to be achieved by the combinedcorrosion-preventing effects thereof. More specifically, the bestcorrosion resistance can be obtained if silica and sparingly solublechromate are employed in the following ratios by weight of nonvolatilematter:

(1) Blocked urethane-modified epoxy resin/(silica+sparingly solublechromate)=90/10 to 40/60; and silica/a sparingly soluble chromate)=90/10to 10/90.

(2) Silica/sparingly soluble chromate acid salt=90/10 to 10/90.

If the ratio of blocked urethane-modified epoxy resin/(silica +sparinglysoluble chromate) exceeds 90/10, the silica and sparingly solublechromate do not exhibit any satisfactory corrosion-preventing effect,but the film has a lower level of corrosion resistance. If their ratiois smaller than 40/60, the blocked urethane-modified epoxy resin failsto be an effective binder, and the paint applied to the film has a lowerlevel of adhesion to it. If the ratio of silica/sparingly solublechromic acid salt exceeds 90/10, or is smaller than 10/90, the combinedeffect thereof is unsatisfactory and the film has a somewhat lower levelof corrosion resistance.

Although silica and/or a sparingly soluble chromic acid salt is theprincipal additive to the blocked urethane-modified epoxy resin, it isalso possible to add, for example, at least one of a silane couplingagent, a color pigment (e.g. an organic pigment of the condensedpolycyclic type, or of the phthalocyanine series), a color dye (e.g. anazo dye, or a dye composed of a complex salt of an azo dye and a metal),a lubricant (e.g. polyethylene wax, fluororesin, graphite, or molybdenumdisulfide), a rust-inhibitive pigment (e.g. aluminum dihydrogentripolyphosphate, aluminum phosphomolybdate, or zinc phosphate), anelectrically conductive pigment (e.g. iron phosphide, or antimony-dopedtin oxide), and a surface active agent.

A roll coater is usually employed for coating the strip with the paintcomposition as hereinabove described, though it is also possible toapply the composition by dipping or spraying and regulate its coatingweight with an air knife, or by roll squeezing. A hot-air,high-frequency induction, or infrared heating oven can, for example, beemployed for heating the strip coated with the paint composition. It isheated to a temperature of from 50° C. to 300° C., and preferably from60° C. to 250° C. If this invention is applied to a steel sheet withbake hardenability, it is preferably heated to a temperature notexceeding 150° C.

Although the steel strip of this invention usually has a layer of zincor a zinc alloy, a chromate layer and an organic resin film on each sidethereof, this invention covers also a strip having a layer of zinc or azinc alloy, a chromate layer and an organic resin film formed only onone side thereof, while the other side thereof consists of a steelsurface, a surface plated with zinc or a zinc alloy, or a surface platedwith zinc or a zinc alloy and coated with a chromate layer.

EXAMPLES

Steel strips plated with zinc or zinc alloys were degreased with analkali, rinsed with water, dried, given chromating treatment, and coatedwith paint compositions by a roll coater, followed by their baking, toprepare coated steel sheet for making automobile bodies.

The resulting steel sheets each coated with an organic composite coatingwere tested for corrosion resistance, image clarity, paint adhesion andweldability. The conditions employed for their preparation were asfollows:

[1] Zinc or a zinc alloy plated steel sheets

Cold rolled steel sheets having a thickness of 0.8 mm and a surfaceroughness (Ra) of 1.0 micron and plated with zinc or zinc alloys wereused as the base materials for the following treatment (see TABLE 1).

[2] Chromating treatment (1) Dried-in-place type chromate coating

A chromating solution having the composition shown below was applied bya roll coater, and dried without rinsing with water. The coating weightof the chromate layer was controlled by varying the ratio in peripheralspeed of the pickup and applicator rolls in the roll coater.

Chromic anhydride: 20 g/l.

Phosphoric acid ion: 4 g/l.

Zirconium fluoride ion: 1 g/l.

Zinc ion: 1 g/l.

Hexavalent chromium/trivalent chromium: 3/3 (by weight).

Chromic acid anhydride/zirconium fluoride ion: 20/l (by weight).

(2) Electrolytic chromate coating

A bath containing 30 g of chromic acid anhydride and 0.2 g of sulfuricacid per liter and having a temperature of 40° C., was used for cathodeelectrolysis at a current density of 10 A/dm² to form a chromate layeron the strip, followed by rinsing with water, and drying. The coatingweight of the chromate layer was regulated by controlling the amount ofthe electric current employed for the electrolysis.

(3) Reacted-in-place type chromate coating

A solution containing 30 g of chromic acid anhydride, 10 g of phosphoricacid, 0.5 g of NaF and 4 g of K₂ TiF₆ per liter and having a temperatureof 60° C. was sprayed on the strip, followed by rinsing with water, anddrying. The coating weight of the chromate layer was controlled byvarying the length of time employed for the treatment.

[3] Organic Resin

The organic resins which were employed are shown in TABLES 2 to 4. Themodified epoxy resins (A₁) to (A₃) and blocked urethanes (B) appearingin the tables were prepared by the processed described below.

(1) Modified epoxy resin (A₁)

A reaction vessel equipped with a condenser, a stirrer and a thermometerwas charged with 1200 parts of a bisphenol A epoxy resin having an epoxyequivalent of 2000, 800 parts of xylene and 1050 parts of cyclohexanone,and they were heated under stirring to form a solution. 36 parts ofisopropanolamine was added, and reacted at 100° C. for five hours toyield a modified epoxy resin A₁ having a resin content of 40%.

(2) Modified Epoxy Resin (A₂)

A reaction vessel equipped with a condenser, a stirrer and a thermometerwas charged with 500 parts of a bisphenol A epoxy resin having an epoxyequivalent of 1500, 385 parts of xylene and 385 parts of cyclohexanone,and they were heated under stirring to form a solution. 20 parts ofisopropanolamine was added, and reacted at 100° C. for five hours, and65 parts of monoisocyanate, which was an addition product of2,4-tolylene diisocyanate having an NCO (isocyanate) percentage of 13%and octyl alcohol, was added for reaction at 60° C. for five hours toyield a modified epoxy resin A₂ having a resin content of 40%.

(3) Modified Epoxy Resin (A₃)

A reaction vessel equipped with a condenser, a stirrer and a thermometerwas charged with 500 parts of a bisphenol A epoxy resin having an epoxyequivalent of 2500, 385 parts of xylene and 385 parts of cyclohexanone,and they were heated under stirring to form a solution. Five parts ofmonoethanolamine was added, and 7.6 parts of dibutylphosphoric acid wasalso added, for reaction at 100° C. for five hours to yield a modifiedepoxy resin A₃ having a resin content of 40%.

(4) Blocked Urethane (B)

A reaction vessel equipped with a condenser, a stirrer and a thermometerwas charged with 440 parts of polyethylene glycol having a molecularweight of 1000 and 125 parts of xylene, and while they were heated at60° C. under stirring, 153 parts of 2,6-tolylene diisocyanate was added,whereby an intermediate having an NCO percentage of 4.8% was obtained.Then, 106 parts of ε-caprolactam was added to continue the reaction, andafter it had been ascertained that the reaction product has an NCOpercentage of 0%, 175 parts of butanol was added, whereby a blockedurethane B1 having a resin content of 70% was obtained.

The same apparatus and reaction conditions were employed to form anintermediate having an NCO percentage of 1.2% from 500 parts ofpolypropylene glycol having a molecular weight of 4000, 300 parts ofxylene and 42 parts of hexamethylene diisocyanate. Then, 23 parts ofmethylethyl ketooxime was added to continue the reaction, and after ithad been ascertained that the reaction product had an NCO percentage of0%, 77 parts of butanol was added, whereby a blocked urethane B2 havinga resin content of 60% was obtained.

The silica added to the organic films is shown in TABLE 5, and thesparingly soluble chromate in TABLE 6.

TABLES 7 to 18 show the details in construction of the coated steelstrips prepared as hereinabove described, and the results of theirevaluation for corrosion resistance (cosmetic corrosion resistance),image clarity, paint adhesion, and weldability. The evaluation for eachproperty was made by the method described below.

(a) Corrosion Resistance (cosmetic corrosion resistance)

Each test specimen was prepared by coating a cationic electrodepositionprimer of U-600, product of Nippon Paint Co., Ltd., with a thickness of25 microns, a sealer of KPX-36, product of Kansai Paint Co., Ltd., witha thickness of 30 microns, and a top coat LUGA BAKE B-531, product ofKansai Paint Co., Ltd., with a thickness of 35 microns. A cross cut wasmade in the specimen with a knife, and the specimen was given 300 or 400cycles of a cyclic corrosion test, each cycle consisting of 10 minutesof a salt spray test, 155 minutes of drying, 75 minutes of a humiditycabinet test, 160 minutes of drying and 80 minutes of another humiditycabinet test. The creepage width from the cross cut in each specimen wasdetermined as a measure of its corrosion resistance (cosmetic corrosionresistance). The results of evaluation are shown by symbols eachrepresenting a certain range of width as indicated below:

: Less than 2 mm:

◯: From 2 mm, inclusive, to less than 4 mm;

Δ: From 4 mm, inclusive, to less than 6 mm;

x: 6 mm or more.

(b) Image Clarity

An image clarity measuring instrument (ICM-2DP) made by Suga TestingMachine Co., Ltd. was employed for forming an image through a 0.5 mmwide slit on each specimen having an cationic E-coat, a sealer and a topcoat formed thereof as described at (a) above, and measuring the clarityC of the image. The results are shown by symbols each representing acertain range of clarity as indicated below:

: 80 or more;

◯: From 75, inclusive, to less than 80;

Δ: From 70, inclusive, to less than 75;

x: Less than 70.

(c) Paint Adhesion

Each specimen having an cationic E-coat, an sealer and a top coat formedthereon as described at (a) above was immersed in ion-exchange waterhaving a temperature of 40° C., and was removed from it after 240 hours.After it had been left to stand at room temperature for 24 hours, 100checkers each measuring 2 mm square were made in the coating and anadhesive tape was attached to, and detached from the coating to evaluateit for its adhesive strength. The results are shown by symbols eachrepresenting the percentage of the coating which peeled off with theadhesive tape:

: No peeling occurred;

◯: Less than 3% of the coating peeled off;

Δ: From 3%, inclusive, to less than 10% of the coating peeled off;

x: 10% or more of the coating peeled off.

(d) Weldability

A continuous spot-welding test was made on each specimen by employing aCF electrode, a electrode force of 200 kgf, a weld time of 10 cycles/50Hz, and a welding current of 10 kA, and the number of the spots whichcould be made continuously on the specimen was counted as a measure ofits weldability. The results are shown by symbols each representing acertain range of the number of spots as indicated below:

: 5000 or more;

◯: From 4000, inclusive, to less than 5000;

Δ: From 3000, inclusive, to less than 4000;

x: Less than 3000.

The following is an explanation of what is meant by *1 to *8 in TABLES 7to 18:

*1: "Inv." means an example of this invention, while "Com." means acomparative example;

*2: The numbers correspond to those appearing in TABLE 1 as identifyingthe plated steel strips;

*3: Each number represents the coating weight of the chromate in termsof metallic chromium;

*4: The numbers correspond to those appearing in TABLES 2 to 4 asidentifying the organic resins;

*5: The numbers correspond to those appearing in TABLE 5 as identifyingthe silica;

*6: The numbers correspond to those appearing in TABLE 6 as identifyingthe sparingly soluble chromic acid salts;

*7: The numbers represent the ratio by weight of nonvolatile matter;

*8: The numbers represent the ratio by weight of nonvolatile matter.

                  TABLE 1                                                         ______________________________________                                        No.  Plated Steel Shoot                                                       ______________________________________                                        1    Zn-12% Ni alloy electroplated steel sheet (coating                            weight: 30 g/m.sup.2)                                                    2    Zn-15% Fe alloy electroplated steel sheet (coating                            weight: 40 g/m.sup.2)                                                    3    Electrogalvanized steel sheet (coating weight: 40 g/m.sup.2)             4    Hot-dipped galvanized steel sheet (coating weight: 90 g/m.sup.2)         5    Galvannealed steel sheet (coating weight: 60 g/m.sup.2)                  6    Two layer galvannealed steel sheet (coating                                   weight: 30 g/m.sup.2)                                                    7    Zn-5% Al-0.5% Mo alloy plated steel sheet made by hot                         dipping (coating weight: 90 g/m.sup.2)                                   8    Zn-60% Mn alloy electroplated steel sheet (coating                            weight: 30 g/m.sup.2)                                                    ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        No.  Modified epoxy resin (A.sub.1)                                                                 Blocked urethane (B)                                                                         A/B                                      ______________________________________                                        1    Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          95/5                                     2    Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          90/10                                    3    Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          70/30                                    4    Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          60/40                                    5    Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          50/50                                    6    Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          95/5                                     7    Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          90/10                                    8    Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          70/30                                    9    Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          60/40                                    10   Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          50/50                                    11   Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          97/3                                     12   Modified epoxy resin A.sub.1                                                                   Blocked urethane B1                                                                          45/55                                    13   Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          97/3                                     14   Modified epoxy resin A.sub.1                                                                   Blocked urethane B2                                                                          45/55                                    ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        No.  Modified epoxy resin (A.sub.1)                                                                 Blocked urethane (B)                                                                         A/B                                      ______________________________________                                        15   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          95/5                                     15   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          90/10                                    16   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          70/30                                    17   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          60/40                                    18   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          50/50                                    19   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          95/5                                     20   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          90/10                                    21   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          70/30                                    22   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          60/40                                    23   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          50/50                                    24   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          97/3                                     25   Modified epoxy resin A.sub.2                                                                   Blocked urethane B1                                                                          45/55                                    26   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          97/3                                     27   Modified epoxy resin A.sub.2                                                                   Blocked urethane B2                                                                          45/55                                    ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        No.  Modified epoxy resin (A.sub.1)                                                                 Blocked urethane (B)                                                                         A/B                                      ______________________________________                                        29   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          95/5                                     30   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          90/10                                    31   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          70/30                                    32   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          60/40                                    33   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          50/50                                    34   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          95/5                                     35   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          90/10                                    36   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          70/30                                    37   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          60/40                                    38   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          50/50                                    39   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          97/3                                     40   Modified epoxy resin A.sub.3                                                                   Blocked urethane B1                                                                          45/55                                    41   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          97/3                                     42   Modified epoxy resin A.sub.3                                                                   Blocked urethane B2                                                                          45/55                                    43   Amine-modified epoxy resin (Japanese Patent Application                       laid open under No. Sho 64-8033, Table 3 No. 2)                          ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        No.  Name                                                                     ______________________________________                                        1    AEROSIL 200 made by Nippon Aerosil Co., Ltd. (silica                          obtained by a dry process)                                               2    AEROSIL 380 made by Nippon Aerosil Co., Ltd. (silica                          obtained by a dry process)                                               3    AEROSIL R974 made by Nippon Aerosil Co., Ltd. (silica                         obtained by a dry process)                                               4    ETC-ST made by Nissan Chemical Industries, Ltd.                               (organoisilica sol)                                                      5    Fine Seal T-32(S) made by Tokuyama Soda Co., Ltd. (silica                     obtained by a wet process of sedimentation)                              6    Syloid 244 made by Fuji-Davison Chemical, Ltd. (silica                        obtained by a wet process of gelling)                                    7    SHIELDEX made by Fuji-Davison Chemical, Ltd.                                  (calcium-exchanged silica)                                               ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        No.  Name                                                                     ______________________________________                                        1    Barium chromate made by Kikuchi Pigment Industrial Co.,                       Ltd.                                                                     2    Strontium chromate made by Kikuchi Pigment Industrial                         Co., Ltd.                                                                3    Calcium chromate made by Kikuchi Pigment Industrial                           Co., Ltd.                                                                4    Zinc chromate (ZTO) made by Kikuchi Pigment Industrial                        Co., Ltd.                                                                5    Potassium zinc chromate (ZPC) made by Kikuchi Pigment                         Industrial Co., Ltd.                                                     ______________________________________                                    

                                      TABLE 7                                     __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    1  Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             2  Inv.                                                                              2    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             3  Inv.                                                                              3    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             4  Inv.                                                                              4    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             5  Inv.                                                                              5    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             6  Inv.                                                                              6    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             7  Inv.                                                                              7    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             8  Inv.                                                                              8    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             9  Inv.                                                                              9    Electro-                                                                           50   3    1   1   60/40 75/25                                                                              0.8                                         lytic                                                             10 Inv.                                                                              1    Reacted-                                                                           50   3    1   1   60/40 75/25                                                                              0.8                                         in-place                                                          11 Com.                                                                              1    Dried-in-                                                                           5   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             12 Inv.                                                                              1    Dried-in-                                                                          10   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             13 Inv.                                                                              1    Dried-in-                                                                          20   3    1   1   60/40 75/25                                                                              0.8                                         place                                                             14 Inv.                                                                              1    Dried-in-                                                                          100  3    1   1   60/40 75/25                                                                              0.8                                         place                                                             15 Inv.                                                                              1    Dried-in-                                                                          200  3    1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             1   ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       2   ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       3   ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ◯                                          4   ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   Δ                                                5   ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ◯                                          6   ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       7   ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   Δ                                                8   ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       9   ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       10  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       11  Δ                                                                            X    ⊚                                                                  ⊚                                                                   ⊚                                       12  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       13  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       14  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       15  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ◯                 __________________________________________________________________________

                                      TABLE 8                                     __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    16 Com.                                                                              1    Dried-in-                                                                          300  3    1   1   60/40 75/25                                                                              0.8                                         place                                                             17 Inv.                                                                              1    Dried-in-                                                                          50   1    1   1   60/40 75/25                                                                              0.8                                         place                                                             18 Inv.                                                                              1    Dried-in-                                                                          50   2    1   1   60/40 75/25                                                                              0.8                                         place                                                             19 Inv.                                                                              1    Dried-in-                                                                          50   4    1   1   60/40 75/25                                                                              0.8                                         place                                                             20 Inv.                                                                              1    Dried-in-                                                                          50   5    1   1   60/40 75/25                                                                              0.8                                         place                                                             21 Inv.                                                                              1    Dried-in-                                                                          50   6    1   1   60/40 75/25                                                                              0.8                                         place                                                             22 Inv.                                                                              1    Dried-in-                                                                          50   7    1   1   60/40 75/25                                                                              0.8                                         place                                                             23 Inv.                                                                              1    Dried-in-                                                                          50   8    1   1   60/40 75/25                                                                              0.8                                         place                                                             24 Inv.                                                                              1    Dried-in-                                                                          50   9    1   1   60/40 75/25                                                                              0.8                                         place                                                             25 Inv.                                                                              1    Dried-in-                                                                          50   10   1   1   60/40 75/25                                                                              0.8                                         place                                                             26 Com.                                                                              1    Dried-in-                                                                          50   3    11  1   60/40 75/25                                                                              0.8                                         place                                                             27 Com.                                                                              1    Dried-in-                                                                          50   12   1   1   60/40 75/25                                                                              0.8                                         place                                                             28 Com.                                                                              1    Dried-in-                                                                          50   13   1   1   60/40 75/25                                                                              0.8                                         place                                                             29 Com.                                                                              1    Dried-in-                                                                          50   14   1   1   60/40 75/25                                                                              0.8                                         place                                                             30 Com.                                                                              1    Dried-in-                                                                          50   43   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             16  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   X                                                      17  ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       18  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       19  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       20  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       21  ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       22  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       23  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       24  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       25  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       26  ⊚                                                                   Δ                                                                            X˜Δ                                                                   ⊚                                                                   ⊚                                       27  X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚                                       28  ⊚                                                                   Δ                                                                            X˜Δ                                                                   ⊚                                                                   ⊚                                       29  X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚                                       30  ◯                                                                      Δ                                                                            X˜Δ                                                                   ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    31 Inv.                                                                              1    Dried-in-                                                                          50   3    2   1   60/40 75/25                                                                              0.8                                         place                                                             32 Inv.                                                                              1    Dried-in-                                                                          50   3    3   1   60/40 75/25                                                                              0.8                                         place                                                             33 Inv.                                                                              1    Dried-in-                                                                          50   3    4   1   60/40 75/25                                                                              0.8                                         place                                                             34 Inv.                                                                              1    Dried-in-                                                                          50   3    5   1   60/40 75/25                                                                              0.8                                         place                                                             35 Inv.                                                                              1    Dried-in-                                                                          50   3    6   1   60/40 75/25                                                                              0.8                                         place                                                             36 Inv.                                                                              1    Dried-in-                                                                          50   3    7   1   60/40 75/25                                                                              0.8                                         place                                                             37 Inv.                                                                              1    Dried-in-                                                                          50   3    1   2   60/40 75/25                                                                              0.8                                         place                                                             38 Inv.                                                                              1    Dried-in-                                                                          50   3    1   3   60/40 75/25                                                                              0.8                                         place                                                             39 Inv.                                                                              1    Dried-in-                                                                          50   3    1   4   60/40 75/25                                                                              0.8                                         place                                                             40 Inv.                                                                              1    Dried-in-                                                                          50   3    1   5   60/40 75/25                                                                              0.8                                         place                                                             41 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   90/10 75/25                                                                              0.8                                         place                                                             42 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   40/60 75/25                                                                              0.8                                         place                                                             43 Com.                                                                              1    Dried-in-                                                                          50   3    1   1   95/5  75/25                                                                              0.8                                         place                                                             44 Com.                                                                              1    Dried-in-                                                                          50   3    1   1   30/70 75/25                                                                              0.8                                         place                                                             45 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 90/10                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             31  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       32  ⊚                                                                   ◯                                                                      Δ                                                                           ⊚                                                                   ⊚                                       33  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       34  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       35  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       36  ⊚                                                                   ◯                                                                      Δ                                                                           ⊚                                                                   ⊚                                       37  ⊚                                                                   ◯                                                                      ◯˜                                                          ⊚                                                                  ⊚                                                                   ⊚                                       38  ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       39  ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       40  ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       41  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       42  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       43  Δ                                                                            X    ⊚                                                                  ⊚                                                                   ⊚                                       44  ⊚                                                                   ◯                                                                      ⊚                                                                  X    ⊚                                       45  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    46 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 10/90                                                                              0.8                                         place                                                             47 Inv.                                                                              1    Dried-in-                                                                          50   3    1   --  60/40 100/0                                                                              0.8                                         place                                                             48 Inv.                                                                              1    Dried-in-                                                                          50   3    --  1   60/40  0/100                                                                             0.8                                         place                                                             49 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.2                                         place                                                             50 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.3                                         place                                                             51 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              1.5                                         place                                                             52 Inv.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              2.0                                         place                                                             53 Com.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              0.1                                         place                                                             54 Com.                                                                              1    Dried-in-                                                                          50   3    1   1   60/40 75/25                                                                              2.5                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             46  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       47  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       48  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       49  ◯                                                                      Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       50  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       51  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       52  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ◯                                          53  X    X    ⊚                                                                  ⊚                                                                   ⊚                                       54  ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   X                             __________________________________________________________________________

                                      TABLE 11                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    55 Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             56 Inv.                                                                              2    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             57 Inv.                                                                              3    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             58 Inv.                                                                              4    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             59 Inv.                                                                              5    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             60 Inv.                                                                              6    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             61 Inv.                                                                              7    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             62 Inv.                                                                              8    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             63 Inv.                                                                              1    Electro-                                                                           50   17   1   1   60/40 75/25                                                                              0.8                                         lytic                                                             64 Inv.                                                                              1    Reacted-                                                                           50   17   1   1   60/40 75/25                                                                              0.8                                         in-place                                                          65 Com.                                                                              1    Dried-in-                                                                           5   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             66 Inv.                                                                              1    Dried-in-                                                                          10   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             67 Inv.                                                                              1    Dried-in-                                                                          20   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             68 Inv.                                                                              1    Dried-in-                                                                          100  17   1   1   60/40 75/25                                                                              0.8                                         place                                                             69 Inv.                                                                              1    Dried-in-                                                                          200  17   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             55  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       56  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       57  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ◯                                          58  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   Δ                                                59  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ◯                                          60  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       61  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   Δ                                                62  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       63  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       64  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       65  Δ                                                                            Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       66  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       67  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       68  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       69  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ◯                 __________________________________________________________________________

                                      TABLE 12                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    70 Com.                                                                              1    Dried-in-                                                                          300  17   1   1   60/40 75/25                                                                              0.8                                         place                                                             71 Inv.                                                                              1    Dried-in-                                                                          50   15   1   1   60/40 75/25                                                                              0.8                                         place                                                             72 Inv.                                                                              1    Dried-in-                                                                          50   16   1   1   60/40 75/25                                                                              0.8                                         place                                                             73 Inv.                                                                              1    Dried-in-                                                                          50   18   1   1   60/40 75/25                                                                              0.8                                         place                                                             74 Inv.                                                                              1    Dried-in-                                                                          50   19   1   1   60/40 75/25                                                                              0.8                                         place                                                             75 Inv.                                                                              1    Dried-in-                                                                          50   20   1   1   60/40 75/25                                                                              0.8                                         place                                                             76 Inv.                                                                              1    Dried-in-                                                                          50   21   1   1   60/40 75/25                                                                              0.8                                         place                                                             77 Inv.                                                                              1    Dried-in-                                                                          50   22   1   1   60/40 75/25                                                                              0.8                                         place                                                             78 Inv.                                                                              1    Dried-in-                                                                          50   23   1   1   60/40 75/25                                                                              0.8                                         place                                                             79 Inv.                                                                              1    Dried-in-                                                                          50   24   1   1   60/40 75/25                                                                              0.8                                         place                                                             80 Com.                                                                              1    Dried-in-                                                                          50   25   1   1   60/40 75/25                                                                              0.8                                         place                                                             81 Com.                                                                              1    Dried-in-                                                                          50   28   1   1   60/40 75/25                                                                              0.8                                         place                                                             82 Com.                                                                              1    Dried-in-                                                                          50   27   1   1   60/40 75/25                                                                              0.8                                         place                                                             83 Com.                                                                              1    Dried-in-                                                                          50   28   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             70  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   X                                                      71  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       72  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       73  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       74  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       75  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       76  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       77  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       78  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       79  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       80  ⊚                                                                   ⊚                                                                   X˜Δ                                                                   ⊚                                                                   ⊚                                       81  X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚                                       82  ⊚                                                                   ⊚                                                                   X˜Δ                                                                   ⊚                                                                   ⊚                                       83  X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 13                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    84 Inv.                                                                              1    Dried-in-                                                                          50   17   2   1   60/40 75/25                                                                              0.8                                         place                                                             85 Inv.                                                                              1    Dried-in-                                                                          50   17   3   1   60/40 75/25                                                                              0.8                                         place                                                             86 Inv.                                                                              1    Dried-in-                                                                          50   17   4   1   60/40 75/25                                                                              0.8                                         place                                                             87 Inv.                                                                              1    Dried-in-                                                                          50   17   5   1   60/40 75/25                                                                              0.8                                         place                                                             88 Inv.                                                                              1    Dried-in-                                                                          50   17   6   1   60/40 75/25                                                                              0.8                                         place                                                             89 Inv.                                                                              1    Dried-in-                                                                          50   17   7   1   60/40 75/25                                                                              0.8                                         place                                                             90 Inv.                                                                              1    Dried-in-                                                                          50   17   1   2   60/40 75/25                                                                              0.8                                         place                                                             91 Inv.                                                                              1    Dried-in-                                                                          50   17   1   3   60/40 75/25                                                                              0.8                                         place                                                             92 Inv.                                                                              1    Dried-in-                                                                          50   17   1   4   60/40 75/25                                                                              0.8                                         place                                                             93 Inv.                                                                              1    Dried-in-                                                                          50   17   1   5   60/40 75/25                                                                              0.8                                         place                                                             94 Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   90/10 75/25                                                                              0.8                                         place                                                             95 Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   40/60 75/25                                                                              0.8                                         place                                                             96 Com.                                                                              1    Dried-in-                                                                          50   17   1   1   95/5  75/25                                                                              0.8                                         place                                                             97 Com.                                                                              1    Dried-in-                                                                          50   17   1   1   30/70 75/25                                                                              0.8                                         place                                                             98 Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             84  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       85  ⊚                                                                   ⊚                                                                   Δ                                                                           ⊚                                                                   ⊚                                       86  ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       87  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       88  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       89  ⊚                                                                   ⊚                                                                   Δ                                                                           ⊚                                                                   ⊚                                       90  ⊚                                                                   ⊚                                                                   ◯˜.circleincircle                                           .   ⊚                                                                   ⊚                                       91  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       92  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       93  ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       94  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       95  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       96  Δ                                                                            Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       97  ⊚                                                                   ⊚                                                                   ⊚                                                                  X    ⊚                                       98  ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 14                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________     99                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 10/90                                                                              0.8                                         place                                                             100                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   --  60/40 100/0                                                                              0.8                                         place                                                             101                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   --  1   60/40  0/100                                                                             0.8                                         place                                                             102                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.2                                         place                                                             103                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.3                                         place                                                             104                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              1.5                                         place                                                             105                                                                              Inv.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              2.0                                         place                                                             106                                                                              Com.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              0.1                                         place                                                             107                                                                              Com.                                                                              1    Dried-in-                                                                          50   17   1   1   60/40 75/25                                                                              2.5                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                              99 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       100 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       101 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       102 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       103 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       104 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       105 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ◯                                          106 X    X    ⊚                                                                  ⊚                                                                   ⊚                                       107 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   X                             __________________________________________________________________________

                                      TABLE 15                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    108                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   2   1   60/40 75/25                                                                              0.8                                         place                                                             109                                                                              Inv.                                                                              2    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             110                                                                              Inv.                                                                              3    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             111                                                                              Inv.                                                                              4    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             112                                                                              Inv.                                                                              5    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             113                                                                              Inv.                                                                              6    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             114                                                                              Inv.                                                                              7    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             115                                                                              Inv.                                                                              8    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             116                                                                              Inv.                                                                              1    Electro-                                                                           50   31   1   1   60/40 75/25                                                                              0.8                                         lytic                                                             117                                                                              Inv.                                                                              1    Reacted-                                                                           50   31   1   1   60/40 75/25                                                                              0.8                                         in-place                                                          118                                                                              Com.                                                                              1    Dried-in-                                                                           5   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             119                                                                              Inv.                                                                              1    Dried-in-                                                                          10   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             120                                                                              Inv.                                                                              1    Dried-in-                                                                          20   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             121                                                                              Inv.                                                                              1    Dried-in-                                                                          100  31   1   1   60/40 75/25                                                                              0.8                                         place                                                             122                                                                              Inv.                                                                              1    Dried-in-                                                                          200  31   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             108 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       109 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       110 ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ◯                                          111 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   Δ                                                112 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ◯                                          113 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       114 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   Δ                                                115 ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       116 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       117 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       118 Δ                                                                            Δ                                                                            ⊚                                                                  ⊚                                                                   ⊚                                       119 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       120 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       121 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       122 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ◯                 __________________________________________________________________________

                                      TABLE 16                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    123                                                                              Com.                                                                              1    Dried-in-                                                                          300  31   1   1   60/40 75/25                                                                              0.8                                         place                                                             124                                                                              Inv.                                                                              1    Dried-in-                                                                          50   29   1   1   60/40 75/25                                                                              0.8                                         place                                                             125                                                                              Inv.                                                                              1    Dried-in-                                                                          50   30   1   1   60/40 75/25                                                                              0.8                                         place                                                             126                                                                              Inv.                                                                              1    Dried-in-                                                                          50   32   1   1   60/40 75/25                                                                              0.8                                         place                                                             127                                                                              Inv.                                                                              1    Dried-in-                                                                          50   33   1   1   60/40 75/25                                                                              0.8                                         place                                                             128                                                                              Inv.                                                                              1    Dried-in-                                                                          50   34   1   1   60/40 75/25                                                                              0.8                                         place                                                             129                                                                              Inv.                                                                              1    Dried-in-                                                                          50   35   1   1   60/40 75/25                                                                              0.8                                         place                                                             130                                                                              Inv.                                                                              1    Dried-in-                                                                          50   36   1   1   60/40 75/25                                                                              0.8                                         place                                                             131                                                                              Inv.                                                                              1    Dried-in-                                                                          50   37   1   1   60/40 75/25                                                                              0.8                                         place                                                             132                                                                              Inv.                                                                              1    Dried-in-                                                                          50   38   1   1   60/40 75/25                                                                              0.8                                         place                                                             133                                                                              Com.                                                                              1    Dried-in-                                                                          50   39   1   1   60/40 75/25                                                                              0.8                                         place                                                             134                                                                              Com.                                                                              1    Dried-in-                                                                          50   40   1   1   60/40 75/25                                                                              0.8                                         place                                                             135                                                                              Com.                                                                              1    Dried-in-                                                                          50   41   1   1   60/40 75/25                                                                              0.8                                         place                                                             136                                                                              Com.                                                                              1    Dried-in-                                                                          50   42   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             123 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   X                                                      124 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       125 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ◯                                          126 ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       127 ◯                                                                      Δ˜◯                                                        ⊚                                                                  ⊚                                                                   ⊚                                       128 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       129 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       130 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       131 ⊚                                                                   ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       132 ◯                                                                      Δ˜◯                                                        ⊚                                                                  ⊚                                                                   ⊚                                       133 ⊚                                                                   ⊚                                                                   X˜Δ                                                                   ⊚                                                                   ⊚                                       134 X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚                                       135 ⊚                                                                   ⊚                                                                   X˜Δ                                                                   ⊚                                                                   ◯                                          136 X˜Δ                                                                    X    ⊚                                                                  ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 17                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    137                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   2   1   60/40 75/25                                                                              0.8                                         place                                                             138                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   3   1   60/40 75/25                                                                              0.8                                         place                                                             139                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   4   1   60/40 75/25                                                                              0.8                                         place                                                             140                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   5   1   60/40 75/25                                                                              0.8                                         place                                                             141                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   6   1   60/40 75/25                                                                              0.8                                         place                                                             142                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   7   1   60/40 75/25                                                                              0.8                                         place                                                             143                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   2   60/40 75/25                                                                              0.8                                         place                                                             144                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   3   60/40 75/25                                                                              0.8                                         place                                                             145                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   4   60/40 75/25                                                                              0.8                                         place                                                             146                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   5   60/40 75/25                                                                              0.8                                         place                                                             147                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   90/10 75/25                                                                              0.8                                         place                                                             148                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   40/60 75/25                                                                              0.8                                         place                                                             149                                                                              Com.                                                                              1    Dried-in-                                                                          50   31   1   1   95/5  75/25                                                                              0.8                                         place                                                             150                                                                              Com.                                                                              1    Dried-in-                                                                          50   31   1   1   30/70 75/25                                                                              0.8                                         place                                                             151                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.8                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             137 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       138 ⊚                                                                   ⊚                                                                   Δ                                                                           ⊚                                                                   ⊚                                       139 ◯                                                                      ◯                                                                      ⊚                                                                  ⊚                                                                   ⊚                                       140 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       141 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       142 ⊚                                                                   ⊚                                                                   Δ                                                                           ⊚                                                                   ⊚                                       143 ⊚                                                                   ⊚                                                                   ◯˜.circleincircle                                           .   ⊚                                                                   ⊚                                       144 ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       145 ⊚                                                                   ◯                                                                      ◯                                                                     ⊚                                                                   ⊚                                       146 ⊚                                                                   ⊚                                                                   ◯                                                                     ⊚                                                                   ⊚                                       147 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       148 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       149 Δ                                                                            Δ˜X                                                                    ⊚                                                                  ⊚                                                                   ⊚                                       150 ⊚                                                                   ◯                                                                      ⊚                                                                  X    ⊚                                       151 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚              __________________________________________________________________________

                                      TABLE 18                                    __________________________________________________________________________                          Organic film                                                        Chromate film          Resin/                                        Divi-                                                                             Base      Weight                                                                             Organic  Chro-                                                                             (silica +                                                                           Silica/                                 sion                                                                              material                                                                           Forming                                                                            (mg/m.sup.2)                                                                       resin                                                                              Silica                                                                            mate                                                                              chromate)                                                                           chromate                                                                           Thickness                       No.                                                                              *1  *2   method                                                                             *3   *4   *5  *6  *7    *8   (μm)                         __________________________________________________________________________    152                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 10/90                                                                              0.8                                         place                                                             153                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   --  60/40 100/0                                                                              0.8                                         place                                                             154                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   --  1   60/40  0/100                                                                             0.8                                         place                                                             155                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.2                                         place                                                             156                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.3                                         place                                                             157                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              1.5                                         place                                                             158                                                                              Inv.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              2.0                                         place                                                             159                                                                              Com.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              0.1                                         place                                                             160                                                                              Com.                                                                              1    Dried-in-                                                                          50   31   1   1   60/40 75/25                                                                              2.5                                         place                                                             __________________________________________________________________________                                 Corrosion                                                                     resistance                                                                    300  400  Image    Weld-                                                  No. cycles                                                                             cycles                                                                             clarity                                                                           Adhesion                                                                           ability                       __________________________________________________________________________                             152 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       153 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       154 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       155 ⊚                                                                   ◯˜Δ                                                        ⊚                                                                  ⊚                                                                   ⊚                                       156 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       157 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       158 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   ⊚                                       159 X    X    ⊚                                                                  ⊚                                                                   ⊚                                       160 ⊚                                                                   ⊚                                                                   ⊚                                                                  ⊚                                                                   X                             __________________________________________________________________________

INDUSTRIAL UTILITY

The coated steel sheet of this invention is useful as a material forautomobiles and electric appliances for domestic use, since it has asurface which is excellent in cosmetic corrosion resistance and imageclarity, as well as in paint adhesion and weldability.

We claim:
 1. An organic composite coated steel sheet, and having thesteel sheet a high cosmetic corrosion resistance and excellent imageclarity, said coating comprising a first layer formed on the surface ofa zinc or a zinc alloy plate steel sheet, and consisting of a chromatelayer having a coating weight of 10 to 200 mg/m² in terms of metallicchromium, and a second layer formed on said first layer, and consistingof an organic resin film containing blocked urethane-modified epoxyresin and a rust-preventing additive in a resin/additive ratio of 90/10to 40/60 (by weight), and having a thickness of 0.2 to 2 microns, saidresin containing a modified epoxy resin (A) which comprises an epoxyresin and a polyfunctional amine, and a blocked urethane (B) whichcomprises a high molecular weight polyol having a molecular weight of400 or above, a polyisocyanate and a blocking agent, in an A/B ratio of95/5 to 50/50 (by weight).
 2. An organic composite coated steel sheet,and giving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity, said coating comprising a first layer formed onthe surface of a zinc or a zinc ally plated steel sheet, and consistingof a chromate layer having a coating weight of 10 to 200 mg/m² in termsof metallic chromium, and a second layer formed on said first layer, andconsisting of an organic resin film containing a blockedurethane-modified epoxy resin and a rust-preventing additive in aresin/additive ratio of 90/10 to 40/60 (by weight), and having athickness of 0.2 to 2 microns, said resin containing a modified epoxyresin (A) which comprises an epoxy resin, a polyfunctional amine and amonoisocyanate, and a blocked urethane (B) which comprises a highmolecular weight polyol having a molecular weight of 400 or above, apolyisocyanate and a blocking agent, in an A/B ratio of 95/5 to 50/50(by weight).
 3. An organic composite coated steel sheet, and giving thesteel sheet a high cosmetic corrosion resistance and excellent imageclarity, said coating comprising a first layer formed on the surface ofa zinc or a zinc alloy plate steel sheet, and consisting of a chromatelayer having a coating weight of 10 to 200 mg/m² in terms of metallicchromium, and a second layer formed on said first layer, and consistingof an organic resin film containing a blocked urethane-modified epoxyresin and a rust-preventing additive in a resin/additive ratio of 90/10to 40/60 (by weight), and having a thickness of 0.2 to 2 microns, saidresin containing a modified epoxy resin (A) which comprises an epoxyresin, a polyfunctional amine and a phosphoric acid, and a blockedurethane (B) which comprises a high molecular weight polyol having amolecular weight of 400 or above, a polyisocyanate and a blocking agent,in an A/B ratio of 95/5 to 50/50 (by weight).
 4. An organic compositecoated steel sheet, and giving the steel sheet a high cosmetic corrosionresistance and excellent image clarity as set forth in any of claims 1,2 or 3, wherein said rust-preventing additive is silica.
 5. An organiccomposite coated steel sheet, and giving the steel sheet a high cosmeticcorrosion resistance and excellent image clarity as set forth in any oneof claims 1, 2 or 3, wherein said rust-preventing additive is asparingly soluble chromate.
 6. An organic composite coated steel sheet,and giving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in any one of claims 1, 2 or 3,wherein said rust-preventing additive is a mixture of silica and asparingly soluble chromate which has a silica/chromate ratio of 90/10 to10/90 (by weight).
 7. An organic composite coated steel sheet, andgiving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in claim 6, wherein said chromatein said organic resin film is barium chromate or strontium chromate, ora mixture thereof.
 8. An organic composite coated steel sheet, andgiving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in claim 5, wherein saidrust-preventing additive is barium chromate or strontium chromate, or amixture thereof.
 9. An organic composite coated steel sheet, and givingthe steel sheet a high cosmetic corrosion resistance and excellent imageclarity as set forth in any one of claims 1, 2 or 3, wherein a blockedurethane-modified epoxy resin contains a modified-epoxy resin (A) and ablocked urethane (B) in an A/B ratio of 90/10 to 60/40 (by weight). 10.An organic composite coated steel sheet, and giving the steel sheet ahigh cosmetic corrosion resistance and excellent image clarity as setforth in any one of claims 1, 2 or 3, wherein said polyfunctional amineis an alkanolamine.
 11. An organic composite coated steel sheet, andgiving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in any one of claims 1, 2 or 3,wherein said epoxy resin has an epoxy equivalent of 400 or above.
 12. Anorganic composite coated steel sheet, and giving the steel sheet a highcosmetic corrosion resistance and excellent image clarity as set forthin any one of claims 1, 2 or 3, wherein said chromate layer is oneformed by coating and has a coating weight of 20 to 100 mg/m² in termsof metallic chromium.
 13. An organic composite coated steel sheet, andgiving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in any of one claims 1, 2 or 3,wherein said epoxy resin has a epoxy equivalent of 400 or above, saidpolyfunctional amine is an alkanolamine, and said modified epoxy resin(A) and said blocked urethane (B) are mixed in an A/B ratio (by weight)of 90/10 to 60/40.
 14. An organic composite coated steel sheet, andgiving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in any one of claims 1, 2 or 3,wherein said chromate layer is one formed by coating and has a coatingweight of 20 to 100 mg/m² in terms of metallic chromium, said epoxyresin has an epoxy equivalent of 400 or above, said polyfunctional amineis an alkanolamine, and said modified epoxy resin (A) and said blockedurethane (B) are mixed in an A/B ratio (by weight) of 90/10 to 60/40.15. An organic composite coated steel sheet, and giving the steel sheeta high cosmetic corrosion resistance and excellent image clarity, saidcoating comprising a first layer formed on the surface of a zinc or azinc alloy plated steel sheet, and consisting of a chromate layer formedby coating and having a coating weight of 20 to 100 mg/m² in terms ofmetallic chromium, and a second layer formed on said first layer, andconsisting of an organic resin film containing a blockedurethane-modified epoxy resin, and silica or a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in a resin/silica or chromate ration of 90/10to 40/60 (by weight), and having a thickness of 0.3 to 1.5 microns, saidresin containing a modified epoxy resin (A) which comprises an epoxyresin having an epoxy equivalent of 400 or above and an alkanolamine,and a blocked urethane (B) which comprises a high molecular weightpolyol having a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight).
 16. Anorganic composite coated steel sheet, and giving the steel sheet a highcosmetic corrosion resistance and excellent image clarity, said coatingcomprising a first layer formed on the surface of a zinc or a zinc alloyplated steel sheet, and consisting of a chromate layer formed by coatingand having a coating weight of 20 to 100 mg/m² in terms of metallicchromium, and a second layer formed on said first layer, and consistingof an organic resin film containing a blocked urethane-modified epoxyresin, silica and a sparingly soluble chromate selected from the groupconsisting of barium chromate, strontium chromate, calcium chromate,zinc chromate, potassium zinc chromate and lead chromate, and having athickness of 0.3 to 1.5 microns, said film containing said resin in aratio of 90/10 to 40/60 (by weight) to the total of said silica and saidchromate, and said silica in a ratio of 90/10 to 10/90 (by weight) tosaid chromate, said resin containing a modified epoxy resin (A) whichcomprises an epoxy resin having an epoxy equivalent of 400 or above andan alkanolamine, and a blocked urethane (B) which comprises a highmolecular weight polyol having a molecular weight of 400 or above, apolyisocyanate and a blocking agent, in an A/B ration of 90/10 to 60/40(by weight).
 17. An organic composite coated steel sheet, and giving thesteel sheet a high cosmetic corrosion resistance and excellent imageclarity, said coating comprising a first layer formed on the surface ofa zinc or a zinc alloy plate steel sheet, and consisting of a chromatelayer formed by coating and having a coating weight of 20 to 100 mg/m²in terms of metallic chromium, and a second layer formed on said firstlayer, and consisting of an organic resin film containing a blockedurethane-modified epoxy resin, and silica or a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in a resin/silica or chromate ratio of 90/10to 40/60 (by weight), and having a thickness of 0.3 to 1.5 microns, saidresin containing a modified epoxy resin (A) which comprises an epoxyresin having an epoxy equivalent of 400 or above, an alkanolamine and amonoisocyanate, and a blocked urethane (B) which comprise a highmolecular weight polyol having a molecular weight of 400 or above, apolyisocyanate and a blocking agent, in an A/B ratio of 90/10 to 60/40(by weight).
 18. An organic composite coated steel sheet, and giving thesteel sheet a high cosmetic corrosion resistance and excellent imageclarity, said coating comprising a first layer formed on the surface ofa zinc or a zinc alloy plated steel sheet, and consisting of a chromatelayer formed by coating and having a coating weight of 20 to 100 mg/m²in terms of metallic chromium, and a second layer formed on said firstlayer, and consisting of an organic resin film containing a blockedurethane-modified epoxy resin, silica and a sparingly soluble chromateselected from the group consisting of barium chromate, strontiumchromate, calcium chromate, zinc chromate, potassium zinc chromate andlead chromate, and having a thickness of 0.3 to 1.5 microns, said filmcontaining said resin in a ratio of 90/10 to 10/90 (by weight) to thetotal of said silica and said chromate, and said silica in a ratio of90/10 to 10/90 (by weight) to said chromate, said resin containing amodified epoxy resin (A) which comprises an epoxy resin having an epoxyequivalent of 400 or above, an alkanolamine and a monoisocyanate, and ablocked urethane (B) which comprises a high molecular weight polyolhaving a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight).
 19. Anorganic composite coated steel sheet, and giving the steel sheet a highcosmetic corrosion resistance and excellent image clarity, said coatingcomprising a first layer formed on the surface of a zinc or a zinc alloyplated steel sheet, and consisting of a chromate layer formed by coatingand having a coating weight of 20 to 100 mg/m² in terms of metallicchromium, and a second layer formed on said first layer, and consistingof an organic resin film containing a blocked urethane-modified epoxyresin, and silica or a sparingly soluble chromate selected from thegroup consisting of barium chromate, strontium chromate, calciumchromate, zinc chromate, potassium zinc chromate and lead chromate in aresin/silica or chromate ratio of 90/10 to 40/60 (by weight), and havinga thickness of 0.3 to 1.5 microns, said resin containing a modifiedepoxy resin (A) which comprises an epoxy resin having an epoxyequivalent of 400 or above, an alkanolamine and phosphoric acid, and ablocked urethane (B) which comprises a high molecular weight polyolhaving a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight).
 20. Anorganic composite coated steel sheet, and giving the steel sheet a highcosmetic corrosion resistance and excellent image clarity, said coatingcomprising a first layer formed on the surface of a zinc or a zinc alloyplate steel sheet, and consisting of a chromate layer formed by coatingand having a coating weight of 20 to 100 mg/m² in terms of metallicchromium, and a second layer formed on said first layer, and consistingof an organic resin film containing a blocked urethane-modified epoxyresin, silica and a sparingly soluble chromate selected from the groupconsisting of barium chromate, strontium chromate, calcium chromate,zinc chromate, potassium zinc chromate and lead chromate, and having athickness of 0.3 to 1.5 microns, said film containing said resin in aratio of 90/10 to 10/90 (by weight) to the total of said silica and saidchromate, and said silica in a ratio of 90/10 to 10/90 (by weight) tosaid chromate, said resin containing a modified epoxy resin (A) whichcomprises an epoxy resin having an epoxy equivalent of 400 or above, analkanolamine and phosphoric acid, and a blocked urethane (B) whichcomprises a high molecular weight polyol having a molecular weight of400 or above, a polyisocyanate and a blocking agent, in an A/B ratio of90/10 to 60/40 (by weight).
 21. An organic composite coated steel sheet,and giving the steel sheet a high cosmetic corrosion resistance andexcellent image clarity as set forth in any one of claims 1, 16, 17, 18,19 or 20, wherein said chromate in said organic resin film is bariumchromate or strontium chromate, or a mixture thereof.
 22. A process formanufacturing a steel strip having an organic composite coating, andgiving the strip a high cosmetic corrosion resistance and excellentimage clarity which comprises chromating the surface of a zinc or a zincalloy plated steel sheet by coating it with a chromating solution, anddrying it without rinsing it with water to form on said surface achromate layer having a coating weight of 10 to 200 mg/m² in terms ofmetallic chromium, coating said chromate surface with a paintcomposition, and baking said composition to form an organic resin filmhaving a thickness of 0.2 to 2 microns on said chromate layer, saidcomposition containing a blocked urethane-modified epoxy resin and arust-preventing additive in a resin/additive ratio of 90/10 to 40/60 (byweight of nonvolatile matter), said resin containing a modified epoxyresin (A) which comprises an epoxy resin and a polyfunctional amine, anda blocked urethane (B) which comprises a high molecular weight polyolhaving a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 95/5 to 50/50 (by weight ofnonvolatile matter).
 23. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 10 to 200 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition to form an organic resin film having a thickness of 0.2 to 2microns on said chromate layer, said composition containing a blockedurethane-modified epoxy resin and a rust-preventing additive in aresin/additive ratio of 90/10 to 40/60 (by weight of nonvolatilematter), said resin containing a modified epoxy resin (A) whichcomprises an epoxy resin, a polyfunctional amine and a monoisocyanate,and a blocked urethane (B) which comprises a high molecular weightpolyol having a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ration of 95/5 to 50/50 (by weight ofnonvolatile matter).
 24. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc ally plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 10 to 200 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition to form an organic resin film having a thickness of 0.2 to 2microns on said chromate layer, said composition containing a blockedurethane-modified epoxy resin and a rust-preventing additive in aresin/additive ratio of 90/10 to 40/60 (by weight of nonvolatilematter), said resin containing a modified epoxy resin (A) whichcomprises an epoxy resin, a polyfunctional amine and phosphoric acid,and a blocked urethane (B) which comprises a high molecular weightpolyol having a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 95/5 to 50/50 (by weight ofnonvolatile matter).
 25. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity as set forthin any of claims 22, 23 or 24, wherein said rust-preventing additive insaid paint composition is silica.
 26. A process for manufacturing asteel strip having an organic composite coating, and giving the strip ahigh cosmetic corrosion resistance and excellent image clarity as setforth in any of claims 22, 23 or 24, wherein said rust-preventingadditive in said paint composition is a sparingly soluble chromate. 27.A process for manufacturing a steel strip having an organic compositecoating, and giving the strip a high cosmetic corrosion resistance andexcellent image clarity as set forth in any of claims 22, 23 or 24,wherein said rust-preventing additive in said paint composition is amixture of silica and a sparingly soluble chromate which has asilica-chromate ratio of 90/10 to 10/90 (by weight).
 28. A process formanufacturing a steel strip having an organic composite coating, andgiving the strip a high cosmetic corrosion resistance and excellentimage clarity as set forth in claim 27, wherein said chromate in saidpaint composition is barium chromate or strontium chromate, or a mixturethereof.
 29. A process for manufacturing a steel strip having an organiccomposite coating, and giving the strip a high cosmetic corrosionresistance and excellent clarity as set forth in claim 26, wherein saidrust-preventing additive in said paint composition is barium chromate orstrontium chromate, or a mixture thereof.
 30. A process formanufacturing a steel strip having an organic composite coating, andgiving the strip a high cosmetic corrosion resistance and excellentimage clarity as set forth in any one of claims 22, 23 or 24, whereinsaid modified epoxy resin (A) and said blocked urethane (B) are mixed inan A/B ratio of 90/10 to 60/40 (by weight of nonvolatile matter).
 31. Aprocess for manufacturing a steel strip having an organic compositecoating, and giving the strip a high cosmetic corrosion resistance andexcellent image clarity as set forth in any of one claims 22, 23 or 24,wherein said polyfunctional amine in said pain composition is analkanolamine.
 32. A process for manufacturing a steel strip having anorganic composite coating, and giving the strip a high cosmeticcorrosion resistance and excellent image clarity as set forth in any ofone claims 22, 23 or 24, wherein said epoxy resin in said paincomposition has an epoxy equivalent of 400 or above.
 33. A process formanufacturing a steel strip having an organic composite coating, andgiving the strip a high cosmetic corrosion resistance and excellentimage clarity as set forth in any one of claims 22, 23 or 24, whereinsaid epoxy resin has an epoxy equivalent of 400 or above, saidpolyfunctional amine is an alkanolamine, and said modified epoxy resin(A) and said blocked urethane (B) are mixed in an A/B ratio of 90/10 to60/40 (by weight of nonvolatile matter).
 34. A process for manufacturinga steel strip having an organic composite coating, and giving the stripa high cosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 20 to 100 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition at a temperature of 50° C. to 300° C. (peak metaltemperature) to form an organic resin film having a thickness of 0.3 to1.5 microns on said chromate layer, said composition containing ablocked urethane-modified epoxy resin, and silica or a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in a resin/silica or chromate ratio of 90/10to 40/60 (by weight of nonvolatile matter), said resin containing amodified epoxy resin (A) which comprises an epoxy resin having an epoxyequivalent of 400 or above and an alkanolamine, and a blocked urethane(B) which comprises a high molecular weight polyol having a molecularweight of 400 or above, a polyisocyanate and a blocking agent, in an A/Bratio of 90/10 to 60/40 (by weight of nonvolatile matter).
 35. A processfor manufacturing a steel strip having an organic composite coating, andgiving the strip a high cosmetic corrosion resistance and excellentimage clarity which comprises chromating the surface of a zinc or a zincalloy plated steel sheet by coating it with a chromating solution, anddrying it without rinsing it with water to form on said surface achromate layer having a coating weight of 20 to 100 mg/m² in terms ofmetallic chromium, coating said chromated surface with a paintcomposition, and baking said composition at a temperature of 50° C. to300° C. (peak metal temperature) to form an organic resin film having athickness of 0.3 to 1.5 microns on said chromate layer, said compositioncontaining a blocked urethane-modified epoxy resin, silica and asparingly soluble chromate selected from the group consisting of bariumchromate, strontium chromate, calcium chromate, zinc chromate, potassiumzinc chromate and lead chromate in such proportions that said resin mayhave a ratio of 90/10 to 40/60 (by weight of nonvolatile matter) to thetotal of said silica and said chromate, while said silica has a ratio of90/10 to 10/90 (by weight of nonvolatile matter) to said chromate, saidresin containing a modified epoxy resin (A) which comprises an epoxyresin having an epoxy equivalent of 400 or above and an alkanolamine,and a blocked urethane (B) which comprises a high molecular weightpolyol having a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight ofnonvolatile matter).
 36. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 20 to 100 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition at a temperature of 50° C. to 300° C. (peak metaltemperature) to form an organic resin film having a thickness of 0.3 to1.5 microns on said chromate layer, said composition containing ablocked urethane-modified epoxy resin, and silica or a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in a resin/silica or a chromate ratio of90/10 to 40/60 (by weight of nonvolatile matter), said resin containinga modified epoxy resin (A) which comprises an epoxy resin having anepoxy equivalent of 400 or above, an alkanolamine and a monoisocyanate,and a blocked urethane (B) which comprises a high molecular weightpolyol having a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight ofnonvolatile matter).
 37. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 20 to 100 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition at a temperature of 50° C. to 300° C. (peak metaltemperature) to form an organic resin film having a thickness of 0.3 to1.5 microns on said chromate layer, said composition containing ablocked urethane-modified epoxy resin, silica and a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in such proportions that said resin may havea ratio of 90/10 to 40/60 (by weight of nonvolatile matter) to the totalof said silica and said chromate, while said silica has a ratio of 90/10to 10/90 (by weight of nonvolatile matter) to said chromate, said resincontaining a modified epoxy resin (A) which comprises an epoxy resinhaving an epoxy equivalent of 400 or above, an alkanolamine and amonoisocyanate, and a blocked urethane (B) which comprises a highmolecular weight polyol having a molecular weight of 400 or above, apolyisocyanate and a blocking agent, in an A/B ratio of 90/10 to 60/40(by weight of nonvolatile matter).
 38. A process for manufacturing asteel strip having an organic composite coating, and giving the strip ahigh cosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 20 to 100 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition at a temperature of 50° C. to 300° C. (peak metaltemperature) to form an organic resin film having a thickness of 0.3 to1.5 microns on said chromate layer, said composition containing ablocked urethane-modified epoxy resin, and silica or a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in a resin/silica or chromate ratio of 90/10to 40/60 (by weight of nonvolatile matter), said resin containing amodified epoxy resin (A) which comprises an epoxy resin having an epoxyequivalent of 400 or above, an alkanolamine and phosphoric acid, and ablocked urethane (B) which comprises a high molecular weight polyolhaving a molecular weight of 400 or above, a polyisocyanate and ablocking agent, in an A/B ratio of 90/10 to 60/40 (by weight ofnonvolatile matter).
 39. A process for manufacturing a steel striphaving an organic composite coating, and giving the strip a highcosmetic corrosion resistance and excellent image clarity whichcomprises chromating the surface of a zinc or a zinc alloy plated steelsheet by coating it with a chromating solution, and drying it withoutrinsing it with water to form on said surface a chromate layer having acoating weight of 20 to 100 mg/m² in terms of metallic chromium, coatingsaid chromated surface with a paint composition, and baking saidcomposition at a temperature of 50° C. to 300° C. (peak metaltemperature) to form an organic resin film having a thickness of 0.3 to1.5 microns on said chromate layer, said composition containing ablocked urethane-modified epoxy resin, silica and a sparingly solublechromate selected from the group consisting of barium chromate,strontium chromate, calcium chromate, zinc chromate, potassium zincchromate and lead chromate in such proportions that said resin may havea ratio of 90/10 to 40/60 (by weight of nonvolatile matter) to the totalof said silica and said chromate, while said silica has a ratio of 90/10to 10/90 (by weight of nonvolatile matter) to said chromate, said resincontaining a modified epoxy resin (A) which comprises an epoxy resinhaving an epoxy equivalent of 400 or above, an alkanolamine andphosphoric acid, and a blocked urethane (B) which comprises a highmolecular weight polyol having a molecular weight of 400 or above, apolyisocyanate and a blocking agent, in an A/B ratio of 90/10 to 60/40(by weight of nonvolatile matter).
 40. A process for manufacturing asteel strip having an organic composite coating, and giving the strip ahigh cosmetic corrosion resistance and excellent image clarity as setforth in any one of claims 34, 35, 36, 37, 38 or 39, wherein saidchromate in said paint composition is barium chromate or strontiumchromate, or a mixture thereof.